Spring loaded intermittent and constant flow gas lift valve and system



LIFT

Jan. 28, 1969 c. M. PETERS SPRING LOADED INTERMITTENT AND CONST ANT FLOW GAS I VALVE AND SYSTEM Filed Feb. 21, 1957 Sheet 5 5 O O O U0 w .w 7 7 O 0 M E 9 I O 7 3 W 0 E W Fm .2 4 5 5 7.. LrLrL.Lr WQJV; II 3 PM o I- w J J l.- JM... |l .MW. M1 D m R .11.111 m m 2 w m. W L m 0 n w 0 I 8 2W2 2 m 4 BY N 4 M 42 ATTORNEYS lor IO5-'/ 109 Jan. 28, 1969 Filed Feb. 21, 1967 C. M. PETERS SPRING LOADED INTERMITTE NT AND CONSTANT FLOW GAS LIFT VALVE AND SYSTEM Sheet 2 of 2 CLIFFORD M. PETERS 1NVENTOR.

BY &

ATTORNEYS United States Patent Ofice A 3,424,099 Patented Jan. 28, 1969 3,424,099 SPRING LOADED INTERMITTENT AND CON-- STANT FLOW GAS LIFT VALVE AND SYSTEM Clifford M. Peters, 16 Rockwall Drive, Longview, Tex. 75601 Filed Feb. 21, 1967, Ser. No. 617,690 US. Cl. 103233 Int. Cl. F04b 39/00; F04f 1/08 9 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention The present invention relates to the field of flowing wells, and more particularly, to a system which incorporates valves which are termed gas lift valves for positioning within a well bore to flow fluids from one or more producing formations within the well bore.

Description of the prior art Various types of gas lift valves have been proposed in the prior art including those wherein valves mounted on a production tubing which is surrounded by a casing with an operating gas pressure being injected into the annulus between the casing and the tubing at predetermined time intervals by a device called an intermitter at the surface. The intermitter is operated generally on a time basis without regard to the well conditions that may change over a period of time. That is, the intermitter is set to operate at a predetermined time interval when it is originally installed; however, over a period of time, the flow conditions of a formation in a well may change, and thus the intermitter permits gas to flow to the annulus in the well bore and actuates the gas lift valves on the production tubing without regard to whether or not there is a column of fluid including gas within the production tubing. Additionally, such installation generally requires that the valves be set to operate at a condition so that the lowermost valve at the bottom or lower end of the production tubing operates at the lowest pressure. This is disadvantageous because of the range of gas pressure that may be required at the surface in order to provide suflicient operating pressure in the lower end of the tubing.

Another type of system of the prior art employs a restricted means such as a choke at the surface which is smaller in discharge capacity than the orifice of the working gas lift valve in the system; and in order to support and lift the column of fluid in the production tubing to the surface when working the bottom emitting valve opens, the valve must be held open for a long period of time. In order to maintain the valve open with the restricted means, a large spread factor must 'be designed into the valve, thereby requiring substantially greater gas usage.

Spread may be defined as the difference between casing pressure when the valve opens and casing pressure when the valve closes. It is generally used in gas lift art as an index to the total amount of gas used from the casing annulus, and it is considered by many to be an important factor in any well flow apparatus and system.

An additional disadvantage of a fixed choke system at the earths surface is that it is impossible to vary the gas rate flow to the well in response to well conditions. Also, it is difficult to change the gas rate flow should the conditions of the well change, and it is not uncommon for such construction to freeze by reason of hydrate formation in the gas or air supply, thereby causing irratic operating conditions.

Generally speaking, gas lif valves in use at the present time endeavor to control the spread of the valve by varying seat size of the valve in relation to the depth at which the valve or valves are to be employed in the well and well conditions. This necessitates the use of multiple seat sizes and requires numerous calculations to ascertain the correct time for holding a valve open to provide sulficient gas to lift a given volume of liquid at varying depths. The operating or bottom valves must be held open until the liquid reaches the surface to perform a complete cycle of lifting a column of fluid to the surface. Gas pressure in the casing annulus is increased to a point above the opening pressure of the operating or bottom valve, and this condition is generally maintained until the slug of fluid in the production tubing reaches the surface. This is disadvantageous because the longer gas pressure acts on the producing formation, or the greater the column of fluid in the production tubing which acts on the producing formation, then, normal flow from the formation is restricted or retarded. Also, it can be seen that this procedure uses excessive gas volume to lift the fluid in the production tubing.

Furthermore, if the spread in the valve is too small, the valve will not stay open the required time to provide suflicient gas or air flow therethrough to lift the slug efficiently to the surface; and as a practical matter, flow apparatus generally may employ excessive spread factors or characteristics to aid in insuring that the slug reaches the surface, thus requiring an excessive use of gas or air. Bellows are an integral part of gas lift valves and are subjected to high differential pressures far in excess of the recommended manufadturers pressure differential which is generally around 350 p.s.i. for a bellows with .72 square inch, and in many cases the bellows are subjected to pressures in excess of 5000 p.s.i. In order to keep the bellows spring rate from being changed under these conditions (which changes the valve setting in a pressure charged valve in a well bore), the prior art has proposed many different bellows protection arrangements to inhibit excessive pressure differential on the bellows, but generally speaking, most arrangements have not proved entirely satisfactory.

Additionally, gas lift valves presently employed in the prior art utilize either pressure charged bellows or nonpressure charged bellows in combination with a spring and where pressure charged bellows are used, they suffer the further disadvantage that they must be charged at the surface of the earth and corrections made for the difference between the temperature of the gas in the dome of the valve at the time that the valve is charged and the temperature of the same gases when the valves are located at various elevations in the well. This requires knowing the exact temperature of the well at valve depth, and on high volume wells makes necessary correct knowledge of the temperature of the moving fluids at valve depth, which is substantially impossible. Charged valves may employ pressure domes of very small volume because of tubing and easing size limitations, and the smaller volume dome is more radically affected by temperature than a larger dome would be. Additionally, the valves must be charged at uniform temperatures while they are handled at the surface during assembly.

Furthermore, the prior art valves are designed either for intermittent flow or for constant flow; however, various prior art devices have been proposed and disclosed as being a valve of a universal type, that is, one that would either permit the well to flow constantly or permit the well to flow intermittently, depending upon the well conditions. However, an analysis of such constructions indicates that they are inoperative for the purposes disclosed, or they suffer severe, typical limitations in actual use.

SUMMARY OF THE INVENTION The present invention is directed to a gas lift valve and system which employs a direct mechanical connection between the spring force and valve stem acting to keep the valve closed and which employs a liquid filled bellows in the valve which has substantially no pressure differential thereacross under all operating conditions.

One of the objects of the present invention is to provide a spring loaded gas lift valve employing a liquid filled bellows to obviate pressure differential thereacross when acted upon by the actuating pressure in the casing annulus and wherein the spread characteristics thereof may be predetermined without regard to well conditions and without employing various size seats to vary the spread characteristics of the valve.

Still another object of the present invention is to provide a spring loaded gas lift valve employing a liquid filled bellows to obviate pressure differential thereacross when acted upon by the actuating pressure in the casing annulus and which may intermit or constantly flow, depending upon the well deliverability conditions.

Yet a further object of the present invention is to provide a spring loaded gas lift valve employing a liquid filled bellows but which does not employ a pressure charge or pressure dome and which provides positive bellows protection.

Still a further object of the present invention is to provide spring loaded gas lift valves employing a bellows with no pressure differential thereacross which close on a drop in casing pressure and even though the well fluids flowing upwardly in the production tubing may not have reached the surface.

Still another object of the present invention is to provide a spring loaded gas lift valve system which may either intermit or constantly flow including a series of tubing and easing pressure control spring loaded valves that automatically supply the required gas into the production tubing beneath the fluid therein through one or more valves depending upon the back pressure in the tubing and pressure in the casing.

Still another object of the present invention is to provide a spring loaded gas lift valve system which may either intermit or constantly flow having a series of tubing and easing pressure control spring loaded valves that automatically supply the required gas into the production tubing beneath the flow therein through one or more valves depending upon the back pressure in the tubing and pressure in the casing and a variable choke at the surface to control the casing pressure surrounding the production string so as to increase or decrease the casing pressure in relation to time and in relation to the fluid column buildup in the production tubing.

Still another object of the present invention is to provide a spring loaded gas lift valve system which may intermit or constantly flow having a series of tubing and easing pressure control spring loaded valves that automatically supply the required gas into the production tubing and a variable choke at the surface to control the casing pressure surrounding the production string so as to increase or decrease the casing pressure in relation to time and in relation to the fluid column buildup in the production tubing and a fluid passage from said production tubing around said variable choke means through which warm we'll fluids may pass to prevent freezing conditions in the variable choke.

Yet a further object of the present invention is to provide a unique spread control in combination with a spring loaded gas lift valve having a liquid filled bellows and still maintain a large throughput or discharge capacity through the flow valve.

Still a further object of the present invention is to provide spring loaded gas lift valves which eliminate the necessity of flow valve seat or orifice calculations or various seat sizes to change the spread factor in an endeavor to supply the necessary gas requirements for various production rates at different well depths.

Other objects and advantages of the present invention will become more readily apparent from a consideration of the following description and drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a quarter sectional view of one form of the upper end of a gas lift valve of the present invention;

FIG. 2 is a quarter sectional view and a continuation of the valve shown in FIG. 1 of the invention;

FIG. 3 is a schematic illustration showing a typical installation of valves of the present invention on a production tubing within a well bore;

FIG. 4 is sectional view illustrating another embodiment of the invention for use in conjunction with a mandrel;

FIG. 5 illustrates a sectional view in the form of a variable choke schematically illustrated in FIG. 1; and

FIG. 6 is another view of the variable choke illustrating the manner of circulating producing well fluids therearound to prevent hydrate formation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS 1 and 2, the valve of the present invention is generally referred to by the letter V and is shown as including a hollow hOUSing 20 having inlet port means 21 for admitting gas into the housing from the area between the production tubing and casing and outlet port means 22 for discharging the gas out of the housing into the production tubing, A valve element referred to generally by the letters VE in FIGS. 1 and 2 is movable longitudinally of the housing 20 to open and close the outlet port 22, thereby controlling flow of gas from the inlet port 21 to the outlet port 22 and into the production tubing.

The housing 20 is divided into a plurality of parts in any suitable manner to accommodate assembly of the valve, and as shown in FIGS. 1 and 2 of the drawings, includes the upper portion 25 which is threaded at its upper end- 26 for receiving the closure 27 having conforming threads 28 which mate with the threads 26 to position the closure 27 within the portion 25 of the housing 20. The internal chamber within portion 25 is at atmospheric pressure. If desired, a seal ring 29 may be provided for inhibiting the passage of well fluids into the portion 20 of the housing when the valve is assembled. The hollow tubular portion 25 is provided with thread 30 at its lower end for engaging with the next adjacent portion of the housing represented at 31 which is provided with threads 32 and 33 for engaging with portion 25 and next lower portion 34, respectively, of the housing 20. Portion 34 of the housing is threaded as illustrated at 36 immediately below the inlet ports 21 for receiving the next portion of the housing represented at 37 which in turn is threaded as shown at 38 for engaging with the threads 36 and the threads 39 for engaging with the threads 40 of the lowermost housing portion 41 which has the external threads 42 thereon for seating in a fitting 0n the production tubing. The valve element VE includes the rod shown in FIGS. 1 and 2 and represented by the numeral 43 which is provided with a conical shaped recess 44 at its lower end for receiving the ball 45 therein.

A piston 46 is provided with a conical shaped portion 47 in its upper end in which the ball 45 is seated, the piston 46 being provided with a recess 48 for receiving a seal ring 49 and a T eflon back-up ring 50 to seal off each end of a liquid filled chamber as will be described more fully hereinafter.

In addition to the members 43 and 46, the valve element VE includes the rod 52 which is threaded at its upper end as shown at 53 for engaging in threaded socket (not shown) in the lower end of piston 46, A cylindrical spacer 55 abuts the lower end of piston 46 and shoulder 52' and surrounds the threads 53 as shown in FIG. 2 of the drawings, and it will be noted that the member 31 is recessed to form a chamber 57 between the spacer and the inner wall of the member 31. In addition, the portion 52 of the valve element VB is smaller in diameter than the portion 31 of the housing 20 to provide a space therebetween represented at 58 which surrounds the portion 52 of the valve element VE.

An annular bellows 60 is sealably connected at its upper end 61 to the shoulder means '63 formed on the portion 31 of the housing and is sealably connected at its lower end 64 to the shoulder means 65 carried on the lower shoulder 62 of portion 52, forming part of valve element VE. Thus, the space 57, space 58, and space 60' formed between bellows 60 and rod 52 form a closed chamber represented generally at 95 for receiving liquid as will be described.

Annular recess or groove 67 is formed adjacent the shoulder 62 of the rod 52 in which is carried suitable seal means such as an O-ring 68, and the edge of shoulder 62 is provided with threads 69 thereon with which is thread edly engaged the cup-shaped member 70 as shown in FIG. 2 of the drawings. If desired, an additional seal 71 may be provided between the lower end of the rod 52 and the member 72 is threadedly engaged with the cupshaped member 70 as shown in the drawings.

The member 72 is provided with a counterbore 73 at its lower end.

Telescopically received within the counterbore 73 is the next portion of the valve element VE represented by the numeral 75, and it will be noted that the upper end 76 thereof is enlarged and is tapered circumferentially as represented at 76 and the enlarged portion 76 is connected within the counterbore 72 by reason of the pin 80 fitting through the wall 81 of member 72 and through an opening formed in the portion 76 telescopically received within the counterbore 73 as shown in FIG. 2 of the drawings. This permits some relative lateral movement between the portion 72 of the valve element VB and the end portion 83 of 75 so that the valve element may firmly seat on the outlet port 22 in the event of any misalignment.

From the foregoing description it can be seen that a solid mechanical connection is provided throughout the extent of the valve element VB, and it will be noted that threads 20a are provided in the housing portion 20 for receiving the adjusting nut 90 to provide a shoulder on the housing 20 for receiving one end 91 of the spring 92 which transmits a force to the valve element VE to urge it to seating position on the outlet portion 22. It will be noted that the lower end of rod 43 is provided with a shoulder 93 against which the other end of the spring is rested, and thus it can be seen that the load of the spring is transmitted directly throughout the extent of the valve element VE to firmly seat it and the adjusting nut 90 may be adjusted to set the spring at any desired pressure which must be overcome by pressure in the casing annulus before the valve will open to permit gas to pass from the inlet port means 21 through the outlet port means 22.

During assembly of the valve, liquid is poured in chamber 95 formed between piston 46 and the bellows 60, as previously described. This liquid is represented by the numeral 95' in the drawings and forms an incompressible medium.

It will be noted that the pressure in the casing annulus acts on the bellows 60 since there is a clearance between members 70, 72 and housing portion 34 to provide a passage 101 whereby gas from the inlet port 21 may act upon the bellows 60; however, any pressure acting on the bellows creates an opposing internal pressure in the liquid within the bellows which is equal to and opposite to the pressure acting thereon so that there is no pressure differential across the bellows. Thus, the valve at all times provides a bellows arrangement which has no pressure differential whether the valve is closed, beginning to open, partially open, or all the way open.

A check valve represented by the numeral 105 is provided below the outlet port 22 and rests on the shoulder 106 formed in the portion 41 of the valve housing 20. The check valve is provided with an end portion 106 which is telescopically received within the bore 107 of the element 108 seated on the shoulder in the housing portion 41 as shown in the drawings, and such end portion is also provided with a seal ring 109 to engage the wall of bore 107 when it is desired to backwash through production tubing for accomplishing a function.

FIG. 4 shows a valve incorporating the features of the valve shown in FIG. 2 with slight modification for operating at higher pressures. The valve again is represented by the letter V, and the valve element is again represented by the letters VE. In this form of the valve, it is illustrated for use in connection wtih a mandrel, the dotted portions 200 representing seals for sealing the valve within the mandrel so that gas may be admitted through the valve and into the production tubing in the desired manner as well known in the art. In the FIG. 4 modification, a portion of the valve housing 200 is represented by the numeral 201 and is threaded as shown at 202 when it is desired to add a cap (not shown) for changing into a nonretrievable form.

The upper end of the valve housing portion 201 is closed off by the plug 203 which is provided with an annular groove 204 and an O-ring seal 205 therein. The plug 203 is provided with threads to threadedly engage with the threads of the housing portion 201 as shown at the upper end of FIG. 4 and an extension 203' projects downwardly, the lower end acting as a stop to limit upward movement of the valve element VE, the same as the lower end 27' of cap 27 limits upward movement of valve member VE in the FIG. 2 form.

In the form of the invention shown in FIG. 4, two springs are employed in order to more readily attain final adjustment of the valve to the desired operating pressure.

Housing portion 201 is shown as being threaded at 205 for connection with the next hollow housing portion 206 which forms gas inlet openings 207 in any suitable form such as slits circumferentially spaced thereabout as shown.

The lower end of the portion 206 is recessed for receiving the seals 200 as previously mentioned and is threaded as illustrated :at 209 for engaging with threads 210 on the housing portion 211. This in turn is threadedly engaged as shown at 212 with the valve housing portion 213 in which is provided a shoulder 214 on which is seated the check valve 215 which performs in a manner similar to that described with regard to FIG. 2.

In the form of the invention shown in FIG. 4, valve element VE includes the piston 220 slidably received within the bore 205a of the housing portion 205 as shown at the upper end of FIG. 4. The piston is provided with a groove 221 and an O-ring seal 222, and a back-up ring 222a for sealing with bore 205a. The upper end of the piston 223 forms a shoulder on which one end 224 of the spring 225 is abutted, and the nut 26 threadedly engaged with the housing portion 201 as shown forms a shoulder portion on the housing for receiving the other end of the spring 225 for urging the piston downwardly along with the other interconnected parts of the valve element VE. The nut 226 may be adjusted along the threads of housing portion 201 to place the desired compression in spring 225.

Connected into the lower end of the piston 220, by any suitable means such as threads or the like (not shown) is a rod 230, or the rod 230 ma be integrally formed with piston 220. It will be noted that the bellows 231 sur' rounds the rod 230 and is spaced therefrom similar in arrangement to the bellows 60 in FIG. 2, and the rod 230 is smaller in diameter than the bore 232. The bellows 231 is connected at one end to the shoulder formed on housing portion 201, and at its other end to the shoulder on cup-shaped member 234. Thus, there is formed between the seal of the piston and bellows 231 a chamber 230a which is filled with liquid 231' when the valve is in seated position.

The cup-shaped member 234 has a circumferential sleeve 235 extending downwardly therefrom. The member 237 has an annular groove 238 therein and the O-ring seal 239 to sealably engage the sleeve 235. A threaded socket 237a receives the threaded end of rod 230, and the recess 230a receives and abuts the upper end of cupshaped member 234 when the valve is assembled. A sleeve 250 surrounds the circumferential depending portion 235 and is radially spaced therefrom as shown in the drawings and is abutted at its upper end against the housing portion 201 as shown in the drawings.

The element 250 provides a shoulder 252 at its lower end against which one end of the spring 253 abuts, thereby providing a shoulder on the housing for receiving the end of the spring, the portion 237 being provided with threads as illustrated at 255 for receiving nuts 256 thereon forming a shoulder means 257 on the valve element VE against which the other end of the spring 253 abuts to urge, along with the spring 225, the valve element VE towards seated position on the outlet 260 in the valve housing.

It can be seen that the operating pressure in the casing annulus is effective on the bellows through the ports 207 and by reason of the radial spacing of the elements 234, 237, and 250. But since the bellows is filled with liquid during assembly and when the valve is seated, any pressure acting on the bellows is counteracted so that the bellows is balanced at all times to prevent any pressure differential thereacross.

It will be noted that the spring loaded valve arrangement of FIGS. 1, 2, and 4 includes an arrangement which in combination with the foregoing described structure enables the valve to operate as a constant flow valve or as an intermitting valve, depending upon well conditions.

The structure may be termed a control bushing and is referred to by the numeral 270 in each FIGS. 1 and 4. It will be noted that the control bushing 270 is formed in the housing portion 37 of FIG. 2 and is formed in the housing portion 211 of the modification shown in FIG. 4 and provides a bore shown at 271 through which a portion of the valve element VE extends.

Bore 271 of the control bushing surrounding the valve element extending therethrough is larger in diameter than the portion of the valve element extending therethrough, but the cross-sectional area of the bore 271 surrounding the valve element VE, minus the cross-sectional area of the valve element extending through the bore 271, is smaller than the cross-sectional area of the outlet port 22 in the FIGURE 2 form or outlet port 260 in the FIG- URE 4 form as will be seen from the statements and examples to follow. As previously noted, the spread of a gas lift valve is defined as the difference between casing pressure when the valve opens and the casing pressure at the time when the valve closes. Therefore, the spread of all previous valves has been the ratio of the valve seat and bellows area.

The present invention changes the spread control of a spring loaded gas lift valve employing a liquid filled bellows from seat and bellows area relationship to the ratio of bellows area exposed to casing pressure when the valve is closed and bellows area when the valve is open. In other words, the difference of seat and stem areas divided by the bellows area.

By way of example only, let us assume in a valve built in accordance with the present invention that the diameter of the outlet port 22 at the seat is *V thus yielding .062 square inch cross-sectional area; let us further assume that the effective stem diameter of the valve element is .218" which is .037 square inch cross-sectional area; let us further assume that the total cross-sectional area of the opening in the means 270 is or .085 square inch cross-sectional area; and let us assume that the bellows area effective or responsive to casing annulus pressure is .29 square inch minus seat area. The present invention then provides a valve which controls spread by the following formula:

S=spread of the valve.

B =area spring force is effective on, to hold valve closed.

Stem =cross-sectional area of the valve stem on which the valve element is carried.

S =cross-sectional area of the outlet port.

.086 or 8.6 p.s.i. per p.s.i. in the casing annulus.

The effective stem cross-sectional area for the purposes of this invention is that cross-sectional area of the stem at the control bushing 27 0.

By comparing the foregoing, it can be seen that the discharge capacity of the valve is .085 square inch-.037 which is equal to .048 square inch, and this is equal to a conventional diameter outlet port with a valve employing a seat having A", spread of 16.3 p.s.i. per 100 pounds casing pressure, and it can therefore be seen that the present invention has cut the spread by approximately /2 without decreasing the outlet port area and therefore uses far less gas from the casing annulus without reducing the gas discharge capacity of the valve.

The present invention also provides a flow apparatus and a resulting system whereby gas or air may be introduced at more than one valve in a gas lift installation in relation to fluid load in the tubing acting to open the valve. It also provides an arrangement whereby fiuid fall back into the production tubing is eliminated, which heretofore might occur when the producing well fluid reaches the well connections at the earths surface which may tend to create some restrictions momentarily.

FIG. 3 represents, by way of example only, a suitable installation which will be first described as an intermitting fiow condition in a well. In Table 1 related to FIG. 3, it is assumed for purposes of illustration that the maximum available lease or kick-off pressure (P is 800 p.s.i. and that therefore the available operating pressure (P is 750 p.s.i. With an operating pressure of 750 p.s.i., the weight of the gas column in the annulus may be calculated by means well known in the art; and in this example results in a casing pressure of 890 p.s.i. at 7,000 feet, assuming a specific gas gravity of .65, surface temperature of 74 F. and temperature gradient of approximately 1.6 F. per 100 depth. FIG. 3 as well as Table 1 reproduced below are also based upon an assumed separator back pressure at the earths surface of 50 p.s.i. It can be appreciated that the figures in Table 1, based on the assumptions noted above, may be calculated by means well known in the art.

Table 1 indicates the pressure in the casing at each valve, the dome pressure, the tubing pressure required to open each valve, and the tubing gradient and fluid pressure required to open the valves at each depth. The data in this chart provides a basis upon which to explain the valve system operation for multipoint injection and its dramatic effects.

TABLE 1 Tubing, p.s.i., Valve Po at Dome, Tubing, p.s.i. between fluid Fluid, Valve No. Depth depth p.s.i. to open valve columns in p.s.i.,

(see below)* produetlon to open ubing Assumed spearator back calculated at .03 p.s.i. plus fluid load in tubing.

Referring to Table 1 and FIG. 3 with pressure on the casing (P reading 750 p.s.i. at the surface, the well fluid pressure required to open valve 8 is 132 p.s.i.; and if this fluid volume is in 2" tubing, it would be approximately 1 /3 barrels of fluid. When fluid rises to this height in the producting tubing, valve 8 will open and allow gas from casing at 890 p.s.i. to transfer into the tubing. This gas acts to start the fluid column moving up the tubing. The column of fluid weighs approximately 440 pounds. Because of the mass inertia of the fluid column and friction' in the flow string, the pressure in the tubing will actually rise to a point above the pressure required to lift the fluid column.

In a conventional valve system single point injection, the valves are set at decreasing pressure down the well bore. To prevent the upper valves from opening when injecting gas through the bottom working valve, usually the lowermost valve has a large port. It is used to provide a fast rate of gas transfer between casing and tubing to insure proper fluid column acceleration without gas breaking through or aerating the fluid. The use of the large port results in a large spread resulting in the use of more gas horsepower than is necessary to achieve the desired results and is therefore very undesirable.

Injection through more than one valve and beneath the moving column of well liquid is made possible in the present system.

The fluid column is moved upwardly in the production tubing 300 by gas transfer from casing annulus 301 to tubing 300 through the working valve, past the next valve up the hole. When the fluid volume in tubing 300 flows past the next valve up the tubing string, it tooopens due to excess tubing pressure and permits gas transfer. Now the rate of gas transfer has doubled from casing to tubing. When the heavy fluid column flows past the third valve up the tubing string from bottom, it opens and the rate of gas has tripled from casing to tubing. This sequence continues until the casing pressure has dropped in relation to the spiral to a point where tubing pressure is inadequate to open the remaining valves and to hold open the valves which are passing gas from casing to tubing. At this point, all valves in the string close; and the gas pressure in the tubing continues to expand and raise the column of fluid the remaining distance to the surface.

When all valves are closed, another column of fluid may then start filling the tubing string from the producing formation. (Note: Valves close on drop in casing pressure.) With all the valves closed, the casing pressure starts to increase. The moving fluid column may have reached the surface, depending upon depth before the valves close or, as in most instances, the valves close; and the increase in pressure in the casing annulus 301 precedes the arrival of the fluid column in the production tubing at the surface. The fluid column arrival at the earths surface is also accompanied by a rapid increase in pressure in the production tubing at the earths surface-usually, an increase of at least between 200 and 400 p.s.i. and maybe more. This increase is a function of various factors including flow line friction and separator back pressure. This high increase in tubing pressure results in opening the top valve in the tubing string under pressure of 50 p.s.i. wet gas gradient in tubing to depth of well low pressure differential and spread between tubing and casing, and enables gas from casing annulus 301 to flow into the production tubing 300. For example, say P has been reduced by 10 p.s.i. due to gas usage. Check #1 valve for P (pressure in production tubing) to open same. Then:

682X.29=772 .224+PT .062=%g= Therefore, with pressure reduced 10 p.s.i. from 750 p.s.i. in the annulus, a raise in tubing p.s.i. of approximately 400 can open the top valve under intermitting conditions and under low differential and spread, adding a boost to the slug.

Also, full spread is only had with zero tubing pressure. Then if the top valve opens, for example with a P of 400 p.s.i. and P 772, 772400=372 p.s.i. .086 (spread of valve)=3l.99 p.s.i. drop in P The resulting transfer of high pressure power fluid such as air or gas from casing annulus 301 to tubing 300 through the upper valve aids in overcoming flow line friction and overcome fluid fall back, thus greatly increasing the mechanical efliciency of the system over the conventional systems in use today.

The following is given by way of further illustration in connection with the example of Table 1 hereina bove.

Mathematical check on well forces expressed in Table 1 force balance equation to determine the tubing pressure necessary to open each valve: P =pressure in valve dome; B =bellows area; B =bellows area exposed to pressure in the casing; Constant Flow: under constant flow conditions where the flow gradient is constant to the surface, pressure in the tubing and casing is almost balanced; gradient pressure on the casing side is slightly higher; additional gas is added to the flow stream to sustain constant flow through the various choke control at the surface. The throughput of gas through the variable choke is always less than the output through the gas lift valve. Therefore, the spread factor built into the flow valve is canceled out and the valve has a throttling type action; P pressure in casing annulus at valve depth; S =seat area; P =pressure in tubing. (Note: P is composed of three forces: #1, separator back pressure; #2, well fluid; and #3, wet fluid gradient of .03 gradient per foot.)

400 p.s.i.

Actual p.s.i.

in tubing between cycles with P reduced 20 p.s.i. from valve for P to open the valve.

773x.29= .23+P .076=479 p.s.i.

gas usage. Check on #6 1 1 tubing under low spread and pressure differentials without paying a penalty in high spread characteristics and resultant excessive gas consumption plus the ability to add a boost to the moving slug when it reaches the surface and encounters increased resistance from flow line friction.

The variable choke 302 may be open so as to allow a more rapid build up of pressure in the casing annulus 301, and this reduces the time interval for the casing pressure increase in the casing annulus 301 during the well fluid build up in production tubing 300 and acts to open the system of valves earlier from the casing side. Therefore, less fluid in the production tubing is required to open the valve, and thus by actuating the system more rapidly, the back pressure effect on the well formation is greatly reduced and thereby creates a faster rate of flow from the formation to the production tubing. It will be noted that the production tubing 300 is connected to surround the variable choke 302 so that warm well fluids may be discharged around the choke 302 to prevent hydrate formation.

The form of the variable choke is illustrated in FIGS. 4 and 5 and includes outer housing 303 in which the production tubing 300 is connected for conducting warm well fluids around the inner housing 304. The inner housing 304 is sealed off relative to and is surrounded by the outer housing 303 in any suitable manner such as that illustrated in FIG. 5. The inner housing 304 is provided with a valve seat 305 and a needle valve 306 thereby controls the flow of power fluid, such as air or gas between the inlet 307 and discharge 308. Thus, the amount of power fluid to the casing annulus 301 to the production tubing 300 can be varied by adjusting the valve element 306, handle 309 connected to 306 is provided for this purpose.

It can be understood that the examples given herein are by way of example only and are not intended to limit the scope of the invention.

The variable choke 302 may be open so as to allow a more rapid build up of pressure in the casing annulus 301, and this reduces the time interval for the casing pressure increase in the casing annulus 301 during the well fluid build up in production tubing 300 and acts to open the system of valves earlier from the casing side. Therefore, less fluid in the production tubing is required to open the valve, and thus by actuating the system more rapidly, the back pressure effect on the well formation is greatly reduced and thereby creates a faster rate of flow from the formation to the production tubing. It will be noted that the production tubing 301 is connected to surround the variable choke 302 so that warm well fluids may be discharged around the choke 302 to prevent hydrate formation.

The form of the variable choke is illustrated in FIGS. 4 and 5 and includes outer housing 303 in which the production tubing 301 is connected for conducting warm well fluids around the inner housing 304. The inner housing 304 is sealed off relative to and is surrounded by the outer housing 303 in any suitable manner such as that illustrated in FIG. 4. The inner housing 304 is provided with a valve seat 305 and a needle valve 306 thereby controls the flow of power fluid, such as air or gas between the inlet 307 and discharge 308. Thus, the amount of power fluid to the casing annulus 301 to the production tubing 300 can be varied by adjusting the valve element 306, handle 309 connected to 306 is provided for this purpose.

It can be understood that the examples given herein are by way of example only and are not intended to limit the scope of the invention.

What is claimed is:

1. A gas lift valve comprising:

(a) a housing having inlet port means for admitting gas into the housing and an outlet port for discharging gas from the housing;

(b) a valve element movable longitudinally of said housing to open and close said outlet port for controlling flow from said inlet port means through said outlet port;

(c) spring means within said housing;

(d) shoulder means formed in said housing and on said valve element whereby one end of said spring abuts said housing shoulder means and the other end abuts said valve element shoulder means to urge said valve element towards closed position position on said outlet port;

(e) bellows means surrounding a portion of said valve element and having one end secured to said valve element and another end secured to said housing, said bellows being exposed to gas admited through said inlet port means;

(f) seal means spaced longitudinally of said bellows between said valve element and said housing for sealing between said valve element and said housing thereby forming a chamber filled with liquid when said valve is seated on said outlet port whereby any force transmitted to said bellows by gas from the inlet port is counteracted by the liquid within the chamber so that there is substantially no pressure differential across said bellows;

(g) said liquid filled chamber being movable within said housing when said valve element moves longitudinally to open and close said outlet port.

2. The invention of claim 1 including in combination therewith a control bushing surrounding said valve element between said inlet and outlet port means and having a surrounding bore larger than the diameter of the valve element extending therethrough, with the cross-sectional area of the bore surrounding said valve element, minus the cross-sectional area of the valve element extending therethrough, being smaller than the cross-sectional area of said outlet port in said housing.

3. The invention of claim 1 including a second shoulder means on said housing and valve element and a second spring seated thereon for urging said valve element towards closed position on said outlet port.

4. The invention of claim 2 including a second shoulder means on said housing and valve element and a second spring seated thereon for urging said valve element towards closed position on said outlet port.

5. Apparatus for use in controlling flow at a subsurface level Within a well conduit in a well bore including adjustable valve means for controlling fluid pressure flow into the well bore surrounding the well conduit, said well conduit conducting well fluids from a subsurface level around said valve means to inhibit hydrate formation thereon, a plurality of spring loaded valve means carried on said well conduit for admitting fluid pressure flow from an outlet port in said valve means into the conduit, each of said spring loaded valves having a housing and a closed chamber formed therein by a bellows filled with liquid when said valve means are seated on said outlet ports to inhibit pressure differential thereacross and each being progressively set to open at a higher pressure within the well bore in relation to their depth in the well bore on the Well conduit so that the uppermost valve is set to .open at the lowest pressure, and said liquid filled closed chambers being movable within said housings when said valve elements move longitudinally to open and close said outlet ports.

6. A combination constant flow and intermittent type gas lift valve comprising:

(a) a housing having inlet port means for admitting gas into the housing and an outlet port for discharging gas from the housing;

(b) a valve element movable longitudinally of said housing to open and close said outlet port for controlling flow from said inlet port means through said outlet port;

(c) spring means within said housing;

(d) shoulder means formed in said housing and on 13 14 said valve element whereby one end of said spring said valve element off said seat for a longer period abuts said housing shoulder means and the other end of time to enable more gas to pass from the inlet to abuts said valve element shoulder means to urge said the outlet port. valve element towards closed position position on 7. The invention of claim 1 wherein said seal means said outlet port; is mounted on said valve element.

(e) bellows means surrounding a portion of said valve 8. The invention of claim 1 including means for adjustelement and having one end secured to said valve eleing said spring means to predetermine the force urged by ment and another end secured to said housing, said said spring means on said valve element. bellows being exposed to gas admited through said 9. The invention of claim 8 wherein said valve element inlet port means; is provided with a connection to accommodate relative (f) seal means spaced longitudinally of said bellows rotation of a portion of said valve element relative to the and carried on said valve element for sealingly enremainder thereof whereby said spring adjusting means gaging with the housing thereby forming a chamber may be rotated to adjust the tension in said spring. for filling with liquid whereby any force transmitted to said bellows by gas from the inlet port is counter- References Cited acted by the liquid within the chamber so that there UNITED STATES PATENTS iaselslglalsstaraitliglly no pressure differential across sa1d 26731568 3/1954 Buffington 103 233 X (g) a control bushing surrounding said valve element ggg between said inlet and outlet port means and having 3175514 3/1965 n 103 232 a bore larger than the diameter of the valve element 3225783 12/1965 Stach fry 6 5 X extending therethrough, with the cross-sectional area 3318258 5/1967 L i a g X of the bore surrounding said valve element, minus 3372650 3/1968 6; 233 the cross-sectional area of the valve element extend- 6207 41 12/1952 G "1 103 233 ing therethrough, being smaller than the cross-seci et tional area of said outlet port in said housing said 2642812 6/1953 Robinson 103233 2,761,465 9/1956 Garrett et a1 137-155 control bushing bore having substantially no pressure drop thereacross when said valve functions as a con- FRED O (MATTERN JR" Primary Examiner. stant flow valve, and said control bushing bore having a pressure drop thereacross when said valve func- WARREN KRAUSS, Assismm Examiner. tions as an intermitting valve to thereby, in effect,

transfer to the area of the bellows that is acted upon us by gas from the inlet port which aids in maintaining 103 232; 137 

